1. Field of the Invention
The present invention relates to a method of finish rolling wire and/or round steel on a continuously operating finish rolling block. The finish rolling block includes a plurality of work rolling sets and sizing rolling sets with essentially round sizing rolls, wherein the rolling sets are arranged closely one behind the other and the rolling planes thereof are alternatingly offset relative to each other by 90.degree.. The invention also relates to a pass arrangement for carrying out the method.
2. Description of the Related Art
Roll pass arrangements of the above-described type are described in German Patent 34 45 219 and have the purpose to manufacture wire and/or round steel with good tolerances, wherein the surface of the rolled material is treated carefully.
All pass arrangements have in common that at least the last pass of the rolling train formed by several roll sets is a finishing pass and has a cross-sectional shape for obtaining the desired finished cross-section of the rolled material.
In a solution known from German Patent 10 73 990, the last sizing pass is preceded by a pass having essentially straight circumferential lines forming the cross-section of an irregular hexagon which subsequently enters the circular sizing pass. It has been found that rolling of the sides of the hexagon is not possible in a single sizing pass. Rather, it has been found that the finished product has dimensional deviations due to flattened portions which remain on the product.
In order to improve the finished cross-section, it is proposed in Iron and Steel Engineer, March 1986, p. 115, to use a pass arrangement in which an oval-shaped transition pass is arranged following the last work pass, wherein the transition pass is followed by two sizing passes having essentially circular pass openings. This arrangement has the problem that the rolled material cannot be held in a stable manner in the round sizing passes. The consequence of this problem is that the wire tilts, i.e. the wire rotates about its longitudinal axis following the oval transition pass, wherein the flat areas created in the region of the gap of the oval transition pass rotate in the first and second sizing passes into the areas of the roll gaps and can remain flat. This problem also cannot be solved with greater pass fillings. Rather, greater pass filling merely result in ledge-like projections in the areas of the roll gaps. In summary, the desired improvement in tolerance cannot be obtained in a pass arrangement which uses two round sizing passes because it is not possible to hold the rolled material in the sizing passes without additional measures.
Because of the negative experiences with the above-described pass arrangement, another proposal provides to arrange as the third-to-last pass a regular hexagon, an oval transition pass as the second-to-last pass and as the last pass a circular finishing pass in the known manner. However, this solution also has the disadvantage that the slightly convexly curved circumferential portions of the rolled material leaving the transition pass end up in the subsequent round finishing pass in the areas of the roll gaps and the finished rolled material is not circular but is flat at the mentioned locations and is of insufficient quality.
In order to solve the problem discussed above, DE 34 45 219 C2 proposes an arrangement which has at the end last passes constructed as sizing passes, wherein the second-to-last sizing pass is dimensioned for an at least 8% reduction and the last sizing pass is dimensioned for a maximum 3.8% reduction, and wherein the third-to-last pass also has a pass opening with straight circumferential lines.
In addition to requiring rolling mills composed of roll sets having three rolls, the solution mentioned last has the disadvantage that rolling of the hexagonal primary material also results in problems in the two round sizing passes with respect to the guidance of the rolled material relative to its longitudinal axis. Accordingly, it is not possible to hold the rolled material in the pass in a stable manner in this known rolling mill.
As is clear from the above discussion of the prior art, it has been a problem for a long time to obtain in rolling mill trains of the above-mentioned type a rolled material which is accurate to size, i.e., is rolled with narrow tolerance fields. The prior art developments show that better results are obtained if more than only one circular sizing pass is used for finish rolling of the wire or round steel. However, the disadvantage for guidance of the rolled material remains. A significant improvement of the quality obtainable by means of precision rolls would be possible if finish rolling of the material can be carried out by means of at least three successive sizing passes using essentially circular pass shapes, without producing quality reductions due to turning of the previously created thickened portion of the rolled material into the areas of the subsequent roll passes in which the thickened portions can no longer be rolled down.